June 12 (Reuters) - In a demand more likely to remainsymbolic than be fulfilled, the U.S. government wants AllenStanford to forfeit $5.9 billion from his massive Ponzi scheme,even though the convicted financier has been declared indigent.

The demand requires court approval, and was made two daysbefore Stanford, who was once considered a billionaire, is to besentenced for operating a multi-billion dollar fraud. Stanford,62, could spend the rest of his life behind bars.

According to a Tuesday filing with the U.S. District Courtin Houston, the government said the $5.9 billion represents asum that Stanford's Antigua-based bank had received frominvestors in certificates of deposit when it was put intoreceivership in February 2009.

Prosecutors said Stanford International Bank Ltd had $7.2billion of CD account balances at that time, of which $1.3billion was fictitious interest.

"While $5.9 billion is clearly a massive amount of money, itis not at all excessive" given Stanford's involvement, U.S.Attorney Kenneth Magidson said in a court filing.

He called the requested amount "conservative," but said itmight be harder to prove a higher amount given the duration ofStanford's fraud and lack of complete records.

Once considered a billionaire but declared indigent in 2010,Stanford was convicted on March 6 by a federal jury on fraud,conspiracy and obstruction charges related to his allegedtwo-decade scam, centered on the sale of bogus CDs.